Multiple stage filter



April 24, 1956 J. P. KOVACS 2,743,017

MULTIPLE STAGE FILTER Filed May 10, 1954 F71. TERED INVENTOR Liv/ UsBifovacs 377,129 filed August 28, 1953.

United States PatentQ 'Ihisinvention relates to improvements in filters,and

more particularly to filtersused in connection with mechanisms whoseoperation is dependent upon the use of :hydraulic operating fluids.-This application is a continuation-in-part of my co-pending applicationSer, No.

. In mechanisms of the type mentioned, for example,

those: involving operation of .aircraft landing gear, aircraft cowlflaps and other aerodynamic surfaces, it is essential. that thehydraulic operating fluid used in these mechanisms be carefully filteredto the finest extent of filtration possible in order to avoid mechanicalfailures of the mechanisms by reason of the presence. of solidimpurities. The avoidance ,of such mechanical failures is especiallyimportant in aircraft. For the fine degree of filtering necessary inorder to keep the hydraulic fluid entirely free of solid impuritieswhich might cause failure of the mechanism, it has been found thatthefiuid must be filtered through a pleated resin-impregnated cellulosictype of filter element such, for example, as the pleated filter elementmanufactured by PurOlator Products, Inc.,

and described in U. S. Patent No. 2,642,187 toBell,

granted June 16, 1953. However,,where the hydraulic fluidmechanisminvolved is used for one of the purposes above referred to, some of thesolid impurities occurring in use of the mechanism have been found to besharp slivers of metal. If the pleated impregnated filterelementabovementioned is used alone in a filtering system usinghydraulicfluid for the purposes mentioned, these slivers frequentlypuncture the filter element which is relatively -fragile and as a resultmaterially impair or destroy the .fine filtering action of the element.Such destruction or impairmentin consequence increases, the hazardsoflmechanical failure of the mechanism,

In order to eliminate this difiiculty and to obviate the puncturinghazards, this invention contemplates protective arrangements in thefilterby way of the use of a -mctallie. edge type filter elementinconjunction with the I pleated cellulosic type of filter elementarranged in such a way with respect to the latter element that the fluidbeing filtered must first pass through the .edge' type 3metalli'celement before its passage through the'cellulosic elements The metallicedge type element hasfiltering interstices that are small. enough to'trap the; harmful -metallic slivers and prevent their reaching thecellulosic element. This eliminates-the hazards of puncturing themetallic slivers have actually gotten. through the firstmentionededgetype metallic element and have punctured ,the cellulosic element, suchslivers and those cellulosic particles tornfrom'the cellulosic elementas a result of its puncture, will be trapped and retained by tlie'seeondvcellulosic element, and ,the latter is entirely freeflto peri :throughwhich the fluid has passed that it must also flow through the secondedge type element. Thus, if by chance ice type filter element and saidsurfacefunctions directlyas aguide or spacer forsaid inner'folds andalso as a reinforcement or support for the entire pleated cellulosicelement This reinforcement or support is of especial advantage Wherefiltration of hydraulic fluids at high pressuresis involved. Theelimination of the spring or perforated cylinder materiallyreduces costsof production of the pleated filter element.

In practicing the invention, the metallic-edge type filter elementswhich have tubular form arearranged concert trically relative to thecellulosic filter element which also 7 has general overallqtubularformso that one of the metallic edge type filter elements lies outwardlyof the outer surface of the pleated cellulosic filter element, and sothat the inner folds of the pleated cellulo'sicv filter element lie indirect contact with the outermost surface of "the I second or innermetallic edge type filter element. The three concentrically arrangedfilter elements in effect provide three step filtration through thefilter in which they arearrangedl This three stage filtration results inincreased safety because more solidparticles or impurities may beremoved: by passage of the hydraulic fluid through the three stages afewer number'of times than would be required it but a singlefiltration'step-we're provided. In practicing the invention thenietallic'edge type filter elements mentioned above may beframe-supported tiype elements such as are shown and described .inLiddell Patent No. 2,042,537, or frameless self-supporting me' tallicedge type filter elements such asshownand described: in Kovacs U. S.Patent No. 2,622,738, or they may be any other suitable type of metallicedgev type filter element of the helically wound wire or disctype'.

Any combination of metallic edge type filter elements I of the typedescribed may be used with the c'ellulosic' type filter element toprovide the composite multi-stagefilter embodying the invention. a

Objects and features of this invention are to provide a filter devicethat will be etfective for use in hydraulic mechanisms of the typehereinabove described and which will adequately and etliciently filterthe hydraulic fluid and remove all dangerous solid impurities that couldcause impairment of function of the hydraulicaliy'operated mechanism. II

, Further objects and features of: the invention 'areto provide filtersutilizing multi-stage filtration whereby the hydraulically operatedmechanism that is being served presence of impurities such as cellulosicfibersor'met'al slivers in the filtered fluid.

Further objects and features of'the invention arethe simplification ofthe structural details of the pleated cellulosic filter element withthe'resultant economies in production and replacement costs.

Further objects and features of the invention are "the provision of amulti-stage filter that is particularlyjuse ful for filtration purposesin high pressure hydraulic systems. Q

Furtlnir objects and features of the invention-are the Patented Apr.,24, 1955] external diameter to provide an annular seat 25.

filtering interstices 27b between adjacent turns.

provision of filter structure providing multi-stage filtration that maybe readily assembled and manufactured cheaply and in which cloggedfilter elements may be readily removed for cleaning or replacement.

Further objects and features of the invention will become apparent fromthe following specification and the accompanying drawings, wherein:

Fig. l is a view partially in vertical section of a filter embodying theinvention; and

Fig. 2 is a transverse sectional view of the filter taken along line 2-2of Fig. 1.

Referring now to the drawings, the reference character denotes thefilter or filter assembly as a whole. This filter 10 comprises a hollowbody or casing 11 and a hollow base 12 with which the casing 11 isthreadedly engaged as will be described. The body or casing 11 assembledwith the base 12 constitutes a filter hous- The base 12 has an opentopped bore 13 that is internally threaded at 14 to receive the threadedportion 15 of the casing 11. The bore 13 extends downwardly in the base12 below the lower open end 16 of the casing 11 to provide a chamber 17.This chamber 17 is in direct communication with the interior 18 of thecasing 11 for purposes presently to be described. An inlet port her inthe base 12 which is separated from the charm ber .17 by the walls ofsaid tubular member 20. An outlet passageway or port 22 is provided in awall of the base 12 and communicates directly with the bore or chamber21. The outlet port or passageway 22 provides for egress of filteredfluid from the filter 10 via the base 12 as will be presently described.

In the embodiment shown, the inlet port 19 and the outlet port 22.areaxially aligned. Such alignment, however, is optional.

A relief valve assembly denoted generally by the reference character 23is provided in the base 12. This relief valve assembly 23 which forms nopart of the present invention is of any conventional type and serves toprovide for direct relief flow of fluid from the inlet port 19 to theoutlet port 22 in the event of clogged conditions of i the filterelements in the filter 10.

The tubular member has a portion 24 of reduced The reduced portion 24 ofthe tubular member 20 serves as a mount for a tubular metallic edge typefilter element 27." This metallic edge type filter element in theembodiment shown is one made in accordance with the teachings of theaforesaid Kovacs Patent No. 2,622,738.

Such metallic edge type filter element 27 generally consists of ahelically wound coil of fiat thin metallic ribbon which has ribs orprojections 27a (see Fig. 2) on one wide face of the ribbon and whichprojections serve to space the adjacent turns of the ribbon and defineAs described in the aforesaid Kovacs Patent, the ribs 27a areappropriately bonded to the smooth wide face of the adjacent ribbon turnso that the entire helix formed by the wound ribbon provides the tubularcompletely self supporting metallic edge type filter element 27. Therelative heights of the ribs 27a of the ribbon and the spacing betweenadjacent ribs determine the size of the filtering interstices.

The tubularself-supporting edge type metallic filter element 27 has oneof its ends positioned on the portion .24 of the tubular member 20 ofbase 12, as seen clearly in Fig. l. The diameter of the filter element27 is such that its end fits tightly on said portion 24 of the tubularmember 20 and a force fit may be used if desired to insure a tightconnection. As seen clearly in Fig. 1, a cap 28 closes off the upper endof the metallic edge type filter element 27 and prevents flow of fluidto be filtered other than through the filtering interstices of said edgetype metallic filter element 27.

A second metallic edge type filter element 30, whose construction islike that of filter element 27 but which is of considerably largerdiameter, is provided. This second metallic edge type filter element 30has ribs 300 and filtering interstices 30/). At its bottom end thefilter element 30 has an end cap 31. Tihs end cap 31 is secured to thebottom end of the filter element 30 as by an annular rim portion 32.This rim portion 32 may be welded or soldered in fixed relationship tosaid lower end of said element 36 in the position shown in Fig. 1. Acentrally located opening 33 is provided in a flange portion 34 of theend cap 31. The opening 33 is dimensioned to fit slidably on the reducedportion 24 of the tubular member 29 so that the flange portion 34 of theend cap 31 rests upon the seat 25. The end cap member 31 thus serves tosupport the tubular metallic edge type filter element 30 concentricallyand in spaced relationship relative to the first-named tubular metallicedge type filter element 27.

An annular ring member 35 is secured adjacent the upper end of thesecond metallic edge type filter element 30, this member 35 beingappropriately fastened or secured as by welding or soldering at 36 tosaid upper end of the filter element 30. An O-ring sealing member 37 iscarried in an appropriate recess provided in the ring 35.

A resin-impregnated cellulosic pleated type filter element 40 is alsocarried removably on the tubular member 20, and as shown this cellulosicfilter element 40 lies intermediate or between the two metallic edgetype filter elements 27 and 30 and in concentric relationship thereto.In general, the pleated cellulosic filter element 40 comprises pleated,phenol formaldehyde resin impregnated cellulosic material, such aspaper. This material, after pleating, is arranged in the form of atubular annulus in which the inner folds 40a and outer folds 40b of thepleats extend substantially in the axial direction of the tubularannulus, and in which the walls or stretches of the pleats aresubstantially radially arranged relative to the axis of said tubularannulus. The open ends of the pleats at the upper and lower ends of thepleatings in the annulus are sealed by respective end caps 43 and 44.The end caps 43 and 44 are appropriately secured to the end edges of thepleats as by cementing for example, as has been described in theaforesaid Bell Patent No. 2,642,187. a

The end cap 43 has a centrally located opening 45. This opening 45 has adiameter which is dimensioned so that end cap 43 will fit slidably onthe reduced portion 24 of the tubular member 20 and rest in a cup 46carrying an O-ring sealing member 47. The cup 46 is mounted on tubularmember 20 to lie between the lower face of the end cap 43 and the upperface of the flange 34 of the end cap 31 of tubular metallic edge typefilter element 30.

The inner metallic edge type element 27 is dimensioned and located inthe center hole of the pleated cellulosic filter element 40 so that theinner folds 40a of the latter lie in direct contact with the outermostsurface of said element 27. The latter surface thus acts as a guide forsaid inner folds 40a and as an inner reinforcement for the entirecellulosic element 40 without requirement for an inner spring orperforated tubular element of the kind described in the aforesaid BellPatent No. 2,642,187. The inner edge type filter element 27 preferablyextends substantially the full axial length between end caps 43 and 44of the pleated cellulosic element 40 and is retained place inside saidpleated element 40 by the end caps 43 into the base 12.

v and 44. Thus, the elements 40 and 27'rnay be mounted on and demountedfromtubular member 20 as a unit for replacement whenever necessary.

The filter casing 11 has an inwardly projecting annular shoulder 51which is so located that it will be tightened against the upper surfaceof annular ring 35' when the casing 11 is threaded into the base 12 thusserving to hold the tubular filter element 30 firmly againstlongitudinal or axial displacement on the tubular member 20.

The upper end cap 44 of the cellulosic filter element 40 fits into acentrally located reduced portion 530i the casing 11 above the shoulder51', and thus the cellulosic filter element 40 is centered at its upperend and maintained in its concentric relationship relative to themetallic edge type filter element 30. The outer foldsv 40b of the pleatsof filter element 40 then lie somewhat spaced from the inner surface ofthe metallic edge type filter element 30, the space being identified bythe reference character 54. If desired, the outer folds 40b may bedimensioned to lie in contact with the. inner surface of outer element30.

The O-sealing ring 55 near the lower end of casing 11 prevents leakageof fluid entering, the base 12 through the port19 around the engagingthreaded portions 14'and 15 of the base 12 and the casing 11. Theupper'end of the casing 11 is provided externally with a wrench engagingprojection 56 to facilitate tightening, of the casing 11 The operationof the filtering, assembly just described is as follows:

The three filter elements 27, 40 and 30 are mounted concentrically onthe tubular member 20 of the base 12 as, described, and the casing -11is then slid over the-assembled filter elements now carriedby tubular.member 20 and is tightened into threaded engagement with the base 12.Inlet port 19 is connected by a conduit (not shown) to the supply sourceof the impure hydraulicfiuid that is to be filtered and the outlet port22 is connected by a conduit (not shown) to eifect delivery of filtered,fluid from filter 10 for use in the hydraulic, mechanism (not shown).

type filter element 30, and after emerging from the inner surface ofsaid element 30 is distributed in the annular space 54 between the outerfold edges b of the pleated cellulosic filter element 40 and said innersurface of said metallic edge type element 30.

In the passage of the fluid through the interstices 30b of the metallicedge type element 30, any large solid impurities therein such as metalslivers are trapped and retained on the outer surface of said element 30as theinterstices 30b of the latter are small enough to preclude theirpassage with the fluid. Thus the fluid reaching the space 54 is free ofsuch metallic slivers and other large impurities which could causerupture and damage to the pleated cellulosic filter element 40. Becauseof end caps 43 and 44 which also act as sealing means, the fluidreaching the space 54 then flows through the pleated cellulosic filterelement 40 before it can reach the inner metallic edge type element 27.In its passage through the pleated cellulosic filter element 40 whoseinterstices are of microscopic size, very fine filtration is efiected,ridding the fluid substantailly of all those of its solid impuritieswhich were not removed by the initial passage through the outer metallicedge type filter element 30. Because of end cap 28 and tight fit ofelement 27 on portion 24 of center tube 20, the filtered fluid orfiltrate leaving the element 40 then can only flow through theinterstices 27b of the innermost metallic edge type filter element 27.The latter element 27 acts as a safety device and the flow therethroughof the fluid leaving element 40 rids such fluid of any metallie sliversthat may have accidentally passed through the outer metallic. element 30and. effected a partial rupture or puncture of the cellulosic element'40. Since inner folds 40b of element 40 lie in direct contact with,filter element 27, the latter reinforces the cellulosic element 40 andmakes it capable of withstanding the disruptive action of high pressurehydraulic fluids. Filter element 27 also traps any cellulosic fibersthat may have been torn'from the cellulosic element 40 by its partialaccidental. rupture. The fluid after passing through the interstices 27bof the inner metallic edge type element 27 passes downwardly into thebore or chamber 21 of the tubular member 20 and from there outwardlythrough the port or passage 22 of the base 12. The filtered fluid orfiltrate emerging from the port of passage 22 is entirely free ofsolidirnt through the outermost edge type metallic filter element 30which rids the fluid of substantially all large harmful impuritiesincluding metal slivers. The second stage is the subsequent passage ofthe fluid through the fine filtering cellulosic filter element 40 which'efiectively rids the fluid of all remaining solid impurities that havenot been trapped in the first stage of filtration. The third stage offiltration is the passage subsequently of the fluid through theinternally located metallicedge type element 27. In the latter stage anyaccidentally passed metallic slivers or cellulosic fibers torn from thecellulosic filterelement40 are trapped. With the construction shown, thepresence of a protective edge type metallic filter elementon each sideof the cellulosic filter element 4'0 also permits reverse filteringaction to be practiced with the filter assembly 10 simply by reversingthe connections to the'respective ports 19 and 22. In that event, theport 22 becomes the inlet port and the port.19 becomes the outlet port.

When the trapped impuritiesclog any of the three filter elements 27, 40or 30, to such an extent that effective filtration is no longerpossible, it is a simple matter to unscrew the casing 11 from its base12 and remove all or any of the clogged elements either for cleansing orfor replacement.

If desired, additional stages of filtration may be provided in a' singlehousing by alternating a plurality of metallic edge type filter elementsand cellulosic type filter elements in any concentric arrangement. 5

While a specific embodiment of the invention has been disclosed anddescribed herein, variations in structural details within the scope ofthe claims are possible and are contemplated. There is no intention,therefore, of limitation to the exact details shown anddescribed.

What is claimed is:

1. A filter assembly comprising a generally cylindrical housing havinginlet and outlet ports, a center tube within said housing communicatingwith one of said ports, a plurality of tubular filter elements withinsaid housing, one of said elements being an edge type element and asecond of said elements being a pleated cellulosic type of elementarranged in the form of a tubular annulus positioned concentricallyabout the tubular edge type element and having its innermost pleat foldsin contact with the outermost surface of said edge type element, saidconcentric, elements being separately insertable into and removable fromthe assembly, and means for directing passage-of fluid to be filteredthat enters the housing via its inlet port successively through all ofthe filter elements before emerging in filtered condition from theoutlet port of said housing.

2. A filter assembly comprising a hollow casing and a base removablyjoined together, said base having a chamber and an inlet portcommunicating therewith, a center tube in said base defining a secondchamber separated from the first-named chamber, said base having anoutlet port communicating with said second chamber, a plurality ofconcentrically arranged, separately insertable and removable filterelements carried by said center tube and extending into said casing, theinnermost of said filter elements being an edge type of filter element,and next adjacent of said filter elements being a pleated cellulosictype of filter element whose innermost pleat folds are in direct contactwith the outermost surface of said edge type filter element, said filterelements being arranged on said center tube so that filtering flow is insuccession from the inlet port through all the filter elements in thecasing and then into the center tube before emerclement concentricallysurrounding said first-named filter element with its innermost folds incontact with the outermost surface of said first-named filter element, asecond tubular edge type filter element concentrically surrounding saidpleated cellulosic type filter element, said concentric elements beingseparately insertable into and removable from the assembly, and meansfor directing filtration flow sucessively through all of the filterelements before emergence of filtrate from the assembly.

4. A filter assembly comprising a housing having inlet and outlet ports,a center tube within the housing communicating with one of its ports, atubular edge type filter element one of its ends mounted on said centertube, an end member for the other end of said element, atubularlyshaped, pleated, cellulosic type filter element concentricallydisposed about said first-named element and having its innermost pleatfolds in contact with the outermost surface of said first-named element,end caps for opposite ends of said pleated filter element to close offopposite ends of .channels defined by its'pleats, a tubular edge typeelement concentrically disposed about the pleated cellulosic filterelement, an end member secured to one end of the secondnamed metallicedge type element and removably mountable on said center tube forsupporting said second-named edge type element from said center tube,and an annular sealing member at the other end of said second-named edgetype element, said end caps, said end member and said sealing membercompelling filtration flow between the inlet and outlet ports of saidhousing in successive stages through the concentrically disposed filterelements, and said concentric elements being separately insertable andremovable from the assembly.

5. In a filter assembly the combination of a tubular edge type filterelement, a pleated cellulosic type filter element arranged in form of atubular annulus positioned concentrically about the edge type elementand having its innermost pleat folds in contact with the outermostsurface of said edge type element, an end cap for one end of the edgetype filter element and end caps for both ends of said cellulosic filterelement, one of said last-named end caps having an opening aligned withthe other end of said edgetype element and whose dimensions and shapecorrespond substantially with those at'said other end of said edge typeelement.

6. In a filter assembly the combination of a tubular edge type filterelement, a pleated cellulosic type filter element arranged in form of atubular annulus whose pleat stretches extend substantially radially ofthe axis of the annulus and whose inner and outer pleat folds extend inparallelism with said axis, said cellulosic element being positionedconcentrically about the edge type element withits inner pleat folds incontact with the outermost surface of said edge type element, an end capcovering one end of the edge type element, and end caps for both ends ofsaid cellulosic element, one of said last-named end caps having anopening aligned with the other end of said edge type element tofacilitate mounting of said two elements as a unit in the filterassembly.

Great Britain Oct. 22, 1952

